• Pesticides eliminate their food, insects and damage their reproductive capacity.
• Loss of habitat - wetlands where swallows used to fly and feed.
• Changes in rural areas - declining human rural population, abandonment of traditional activities and new styles of architecture, together cause loss of suitable nesting sites.
• Lack of mud in urban environments make it difficult for swallows to build their nests.
• The Sahara Desert is expanding - meaning that swallows face a tougher migration and can die from heat and exhaustion.
• Climate change:
  
  • In Africa and on migration routes, climate change can have a serious impact. Research has shown that swallows are returning to their breeding areas in poor condition and laying fewer eggs than in the past.
  • The adverse weather conditions in Europe are affecting swallows: Cold seasons with recent frosts are difficult for these small birds.
  Hot, dry summers mean that water troughs where insects are present dry out and nests can die from overheating.
  Constant rainfall over long periods of time makes it difficult for adult swallows to find food, and some die as a result.
• Predation:
  Nests are often attacked by rats, mice and snakes that eat the eggs and chicks while predators attack the young. Birds of prey such as hawks, owls and eagles can take all the young from a nest, leaving no trace.
• Destruction of nests by other species:
  House martins and crag martins are known to occasionally take over the nests of barn swallows, sometimes destroying the eggs in the process.
• Young swallows may fall out of their nests while other juvenile deaths may be due to intense heat or severe cold, nest fall and nest collapse.
• Nests are susceptible to external pests. Colonies cannot rebuild due to heavy infestations and if pest populations become excessive, they will prematurely abandon their nests leaving the young. Characteristic small holes in their wings and tail feathers appear to be caused by bird lice.
• Human causes:
  Because barn swallows nest in close proximity to humans, nests may fail due to intentional disturbance or destruction or unintentional disturbance by human activities near the nest.